The bishop says that if the marriage equality referendum is passed on May 22 it will 'change the meaning of marriage in the Irish Constitution, and as understood by society for centuries'.

'If carried, the referendum will redefine our understanding of marriage, from a unique relationship different from all others, to being another adult relationship regardless of gender,' the bishop says in a pastoral letter to the Diocese of Ferns.

'The American Chief Justice John Roberts responding to proponents of same-sex marriage summed it up like this "you're not seeking to join the institution, you're seeking to change what the institution is. The fundamental core of the institution is the opposite-sex relationship and you want to introduce into it a same-sex relationship.

'An essential characteristic of marriage is that it is open to the generation of new life and the union of man and woman in marriage is usually blessed with the gift of children.'

Bishop Brennan says children have 'a natural right to a mother and a father. Sometimes, unfortunately due to circumstances beyond everybody's control this does not obtain, but this is quite different from legislating to make it impossible for some'.

'As the Bishops say in 'The Meaning of Marriage' - "male - female complementarity is intrinsic to marriage... the true nature of marriage, lived in openness of life, bears witness to how precious Is the gift of a child and to the unique roles of a mother and father.

'Marriage of course is not merely a private affair. Marriage involves society and indeed in time becomes society. For this reason marriage is given special recognition in our Constitution where it says "the state pledges itself to guard with special care the institution of marriage, on which the family is founded and to protect it against attack." (Art.41.3.1)'.

On 22 May the people will be asked to decide the matter. In the meantime I ask everyone to ponder the issues involved and I say to all voters: Marriage is important - it has served us well - Reflect before you change.'